JAWS OF THE ECHINUS. 91 



parently most remote, and organs destined for widely dif- 

 ferent uses: so that even when there lias l)een a complete 

 change of purpose, we still perceive the same design fol- 

 lowed, the same model copied, and the same uniformity of 

 plan preserved in the construction of the organs of every 

 kind of mastication; and there prevails in tiicm the same 

 unity of system as is displayed in so marked a manner in 

 the conformation of the organs of progressive motion. The 

 jaws, which, in one tribe of insects, are formed for breaking 

 down and grinding the harder kinds of food, are, in another, 

 fitted for tearing asunder the more tough and fd^rous tex- 

 tures; they are fashioned, in a third, into instruments for 

 taking up the semi-fluid honey prepared by flowers; while, 

 again, in a fourth, they are prolonged and folded into a tu- 

 bular proboscis, capable of suction, and adapted to the drink- 

 ing; of fluid aliment. Pursuino; the examination of these or- 

 gans in another series of articulated animals, we And them 

 gradually assuming the characters, as well as the uses, of 

 instruments of prehension, of weapons for warfare, of pillars 

 for support, of levers for motion, or of limbs for quick pro- 

 gression. Some of these remarkable metamorphoses of or- 

 gans have already attracted our attention, in a former part 

 of this treatise.'* Jaws pass into feet, and feet into jaws, 

 through every intermediate form; and the same individual 

 often exhibits several steps of these transitions; and is some- 

 times provided also with supernumerary organs of each de- 

 scription. In the Arachnida, in particular, we frequently 

 meet with supernumerary jaws, together with various ap- 

 pendices, which present remarkable analogies of form with 

 the attennse, and the legs and feet of the Crustacea. 



The principal elementary parts which enter into the com- 

 position of the mouth of an insect, when in its most perfect 

 state of development, are the seven following: a pair of up- 

 per jaws, a pair of lower jaws, an upper and a lower lip, and 

 a tongue.t These parts in the Locusta vhHdisswia, or com- 



♦ Vol. i. p. 206. 



f All these parts, taken together, were termed by Fabriclus ijistrumcnla 



